How to Construct a Solar Water Heater

Employing solar power to heat water symbolizes one of the most logical methods of generating hot water that you can find. Why use un-renewable resources when we have an over abundance of energy emitting from our own sun? It is rapidly becoming an acknowledged impression that the best way to diminish energy consumption is by building your own.

During the construction phase of this project, you would need to paint your water tank with flat stovepipe black paint. The paint will permit the tank to absorb as much of the sun's energy as it can. You will also need to assemble a straightforward plywood box around the water tank. Be sure to insulate the interior of the box with some fiberglass insulation, as this will facilitate eliminating any energy lost within the system.

At this point in time, you would install the painted water tank into the box and attach any of the necessary plumbing to the bottom of it. These are, of course, the pipes which carry the water from your house to the heater. Another set of water pipes will carry the water from the heater back to the houses water distribution system.

Here you have a simple home made solar water tank that is more then capable of providing a single person or perchance a couple with adequate quantities of water.

Where I live, even the best, most efficient solar panels, tank, controls etc will at best only produce 30 to 35% of the required domestic hot water. At an average installed cost of around $ 14,000.00 there is no pay back at all, but at leas you get a warm fuzzy feeling when you tell other folks how "green" you are. In India, where the sun shines more often and at a better solar azimuth, you have a much better chance of sucess.

I can see where that would be a problem for you living in 'South Maine' . . . . that's a lot like 'Northern Massachusetts' - What little sunshine you get is from a terrible angle, especially if it's not summertime

Down here on the Gulf Coast we get more hot water than we know what to do with about 10 months of the year from a single 4 by 10 AET panel feeding a couple of 55 gallon water heaters used as storage tanks - The other 2 months, we use a timer to add about 15 minutes worth of electricity to the top element of the house tank just before we arise and that (plus the solar gain during the day) gives us plenty of hot water even in the dead of winter

I installed it all myself for less than $3K, got an 'Instant Rebate' from Uncle Sam which covered over half the cost and had it completely paid off with the energy saved in less than 3 years - It's all gravy from that point on. I guess you could say 'green gravy' because it saves us at least $50 per month

I can't compute how much production he gets with a black tank in a box mounted up on the roof . . . . but I imagine it cost him so little to do that the payback will be quite short. The downside as I see it is that the uninsulated tank will give away most of it's heat overnight, leaving you to basically start all over the next day. I'd make sure the roof is capable of handling the extra weight before I began such a project though . . . . my 110 gallons of tankage might be a problem for most roofs

Where I live, even the best, most efficient solar panels, tank, controls etc will at best only produce 30 to 35% of the required domestic hot water. At an average installed cost of around $ 14,000.00 there is no pay back at all, but at leas you get a warm fuzzy feeling when you tell other folks how "green" you are. In India, where the sun shines more often and at a better solar azimuth, you have a much better chance of sucess.

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It's less about panel efficiency than it is about dollar efficiency. Where you have the space for more square feet of cheaper, somewhat lower efficiency collectors, DIY hackers can (and do) get a lot more than 35% for a heluva lot less than $14KUSD, even in places with cooler winter temps & higher latitudes than New England:

It takes a bit of design & measurin' skills to get away with using PEX as your tubing in a DIY collector though- pay close attention to stagnation temps, and be sure to angle steeply enough that late summer stagnation temps don't go over 200F. The melting temp of PEX is ~260F, but you don't want to deal with steam pressurization on an otherwise atmospheric pressure system like that homebuilt drainback. (Non-ferrous pumps are also important in an atmospheric-pressure system as well, since it's oxygen-rich, and will eat susceptible metals fast.)

Also key to the performance of that system is the oversized thermal storage (~180 gallons), which allows the collectors to run at lower average temps (==higher efficiency), as well as letting the system to coast through some low-input days and still have something left to deliver. Somewhat bigger storage would probably be needed to get that kind of winter performance in New England, or for hot-water hoggin' 5 person families, but more than 100gallons/person would be overkill for most.

It takes a pretty lousy designer/installer to spend anything like $14k to deliver a mere 1/3 of annual hot water needs, even in New England, IMHO. But in many/most cases there's much better ROI on drainwater heat recovery (~20% energy-use reduction for under $1k is typical). In not-so-sunny central MA the typical installed price for solar hot water systems is more like $7k (before subsidies), and deliver more than 60% of the annual hot water. That's twice the fraction, half the cost, for 4x the BTUs/$ of your straw-man system, but nowhere near the BTUs/$ performance of drainwater heat recovery.

If you're going with commercial (as opposed to DIY) solar thermal, you can buy an EnergyStar washer & dishwasher for the price of the solar thermal required to support the load difference between those and your 15+ year old clunky hot-water hogs. As with anything solar, reducing the actual load by half or more is usually more cost effective than just buying more & more solar. Once your DHW load is under 10MBTU/year, the size & cost of the solar necessary to run it becomes manageable. If you're planning on heating the outdoor hot tub with it all winter, well... (yer kinda askin' for it.)

1 - You absolutely can not use pex in a collector and anywhere else in the high side of the system for two reasons. within the panel, Pex is an bad conductor of heat so it's efficiency would be just plain awful and typical temperatures can run well over 300 degrees which puts it twice what pex is rated for.

2 - If you can get a 3 panel set with tank and controls for under 7 grand without subsidies then you need to PM me and give me the name of your supplier because I can't buy the equipment for that price.

3 - Try this web site www.caleffi.com and download idronics 3. Read it and get back to me.

4 - Been installing solar systems since the early 70's Not much I don't know about them and believe me, I've seen it all.

5 - Guys that build their own stuff will always tell you how wonderful it is. People that spend a lot of money to have it installed will always tell you how wonderful it is. That's because they have an investment in it. It's just human nature.

The performance curves and case studies from all over Europe are on the web and available to you. I strongly recommend that anyone considering solar, take a few days and do the research.

I don't think PEX would work well either . . . . but whatever you used in a home made collector, I'd assume it would be painted black before you closed it up and that should take care of any UV exposure

I didn't use PEX anywhere in my system largely because I just didn't trust it with 212 degree temperatures coupled with 60 pounds of pressure . . . . likely that pressure goes way up when the water starts to boil too

My tubing runs to and from the collector are soldered 1/2 inch rigid copper, insulated and placed inside 1 1/2 inch PVC pipe - I've had a couple people comment that my 1 1/2 inch lines are pretty big . . . . until I explain that there's insulated 1/2 inch copper inside them. If you can imagine how thrilling it must have been to solder on a piece, insulate it, slide a piece of 1 1/2 inch PVC over it . . . . complete with 90 degree fittings and then move on to the next connection then you're right - It was quite a challenge. I only did it after I had sweat soldered together about 200 connections without a leak when I was re-plumbing the house - Still, it was an apprehensive moment when we fired up the solar panel checking for any water running out of the end of the PVC - Fixing a leak at that point would have been . . . . problematic

...angles the collector so that the stagnation temps never exceed 200F (Wirsbo has sample of PEX that's been running at a bit over 200F for 25 years and counting)...

...runs them at atmospheric pressure...

...and they work.

Is it ideal? Not even.

Is it anything I'd want to support, as commercial installation? Nope!

But it works, and it's cheap. (I warned him off of using PEX the day he put the design concept on his site, but did he listen? Not much! )

But you don't have to go that cheap, and you get WAY better than 30% of your hot water in New England for $14K straw-man solar price tag (unless you're a hot-water pig, of course. Don't plan on fillin' the 120gallon spa with endless solar HW.) And it shouldn't take anything like 3 panels worth either.

I refer you to figure 35 page 31 of idrionics 3.

A single 40 square foot panel with a paltry 60 gallons of storage in Boston (the closest latitude/weather to Southern Maine listed) will yield roughly a 50% fraction for 80-gallon/day users, or a ~70% fraction for the same system for 40 gallon/day hot water sippers. My family's use is somewhere in between, which means we'd more likely to see something like a 60% fraction with that minimalist system- more if we went with bigger storage to be able to run lower collector temps. This isn't rocket science.

If that costs FOURTEEN THOUSAND 'MERICAN SHEKELS installed, I'm in the wrong business. And if it's only a 30% fraction either the installer/designer fugged up, or you're not at all conservative in your hot water use. The US average is 15-30 gallons/person/day. It takes a lot less money to implement easy reductions in volume used than it does to buy more solar to support a ridiculously heavy load. (Buy a front-loading washer and check the flow on the shower heads before you buy the first panel.)

Gia-normous unpressurized tanks like Reysa's are cheap, and increase the average collector efficiency by keeping the delta-Ts bounded. And with collectors as cheap as his, more square footage isn't very extravagant, nor is the sub-par performance per square foot much of an issue. Performance per dollar is pretty good. But I'm repeating myself...

But none of it has the ROI of drainwater heat recovery- couldn't imagine doing anything solar without going there first. For under a grand in hardware you get the first ~20% fraction. (This assumes national average usage, where showers are 40% of hot water used, and the flow runs at 2.5gpm or less so that the more than 50% of the heat is directly returned to the system.)

Building your own would be a perfect idea but of course before you can make it possible you will need to have certain knowledge about it well don't worry too much about it the internet can be a good source for the info you will need

The bottom line is there is no savings on these systems. They break down long before you get any pay back. Some day there maybe when the cost comes down. As far as government pay backs, that's another big problem that I won't get into here.

Cheap plastic unglazed pool heater systems are one thing, professionally installed rooftop mounted potable systems in deep-freeze & hail/hurricane country quite another. Maintenance & damage in excess of fuel savings are common (though not the rule). It still takes a high-fuel price to rationalize the upfront costs & maintenance expense. If you're on the natural gas grid and paying $1/therm, the net present value of the fuel savings against the the cost of money isn't likely to be positive at full retail installation & maintenance. One $200 service call wipes out more than a year's fuel savings(!). But cheap DIY hacks, self-maintained can be cost effective. If it's replacing electric hot water on an isolated island power grid @ 40cents/kwh the economics of commercial systems are compelling enough.

On the commercial end, plastic flat-plate batch-solar pre-heat in the non-freeze south is usually cost effective: No pumps, no glycol loops to maintain, no heat dumping required, simple-as-pie plumbing, they just work. If you're in an area that get's baseball sized hail it could be an issue though. The Harpiris SunCache and it's ilk would probably be reasonable bets even in the Pacific Northwest (west of the Cascades, at sub-1000' altitudes, but alas not freeze-proof enough for New England winter temps.) The greater the complexity, the greater likelihood of making it a losing proposition. Any batch solar hot water (flat plate or evacuated tube) is pretty simple, cheap, & reliable relative to drainbacks & glycol loops with pumps, sensors & electronic control failure modes.

I have 2, 3 by 8 collectors, one soft tank, and one differential controller that have been in operation since 1991. Its a drain back system with a 007 Taco bronze pump. I have had a homemade heat exchanger leak in the tank from using copper wire to tie it up. Other than that, the system has had 0 maintenance. I live in Maine, is that cold enough for ya?

I have 2, 3 by 8 collectors, one soft tank, and one differential controller that have been in operation since 1991. Its a drain back system with a 007 Taco bronze pump. I have had a homemade heat exchanger leak in the tank from using copper wire to tie it up. Other than that, the system has had 0 maintenance. I live in Maine, is that cold enough for ya?

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You might be close to breaking even by now then, eh? (Or not, depending on how much hot water you actually use, what fuels you would have otherwise paid for and how much you had to pay for the repair when the heat exchanger problem. If it's was a DIY repair to a DIY HX, this doesn't qualify as "full retail" solar, not even close.) And if you're near the coastal hurricane zones, collector-longevity might be much better some decades than others...

At full-retail with fat-margins for the manufacturers & installer, $14KUSD up front for a net thermal input of ~10-15MBTU/year, maybe not... (depends on the discount rate and energy price inflation and mainenance cost assumptions in your net-present-value analyis.)

At $5KUSD- maybe- depends on the cost of energy from other sources, and the maintenance cost over the anticipatied lifetime of the equipment. It's still not a no-brainer.

But I DO want to know the truth, so show me the math. (Self-maintained DIY systems for under $2.5KUSD, no argument whatsovever, eh?) The math will set you free...